1. FIELD OF THE INVENTION
This invention relates to an economically advantageous process for preparing a high purity p-vinylphenol polymer from crude p-ethylphenol in fewer steps.
2. DESCRIPTION OF THE PRIOR ART
It has been difficult to obtain high purity p-vinyl-phenol polymer; in fact, no commercial production is now practiced. According to conventional polymer production techniques, high purity p-vinylphenol polymer can generally be prepared as follows: First, crude p-ethylphenol is purified to form high purity p-ethylphenol. This step is required in order to remove m-ethylphenol and o-ethylphenol inevitably formed in producing crude p-ethylphenol. For example, in the productin of p-ethylphenol by sulfonating ethylbenzene and then subjecting the resulting product to alkali fusion, i.e., reaction of the resulting product with an alkali hydroxide in the fused state, the resulting crude p-ethylphenol contains about 5% (unless otherwise specified, all percentages in the specification are by weight) m-ethylphenol, about 5% o-ethylphenol, and some amounts of impurities such as phenol or cresol. The resulting high purity p-ethylphenol is then dehydrogenated to p-vinylphenol. The crude vinylphenol obtained contains phenols (phenols other than p-vinylphenol) such as unreacted p-ethylphenol, phenol or cresol, water and p-vinylphenol oligomers or low molecular weight polymers in addition to p-vinylphenol. The composition of the crude vinylphenol obtained by dehydrogenation varies greatly according to the dehydrogenation conditions. One example of the composition of the crude p-vinylphenol is 46.0% p-ethylphenol, 15.4% p-vinylphenol, 1.2% other phenols, 5.0% water, 0.6% p-vinylphenol oligomers or low molecular weight polymers, and 31.8% benzene. The benzene is generally introduced in the dehydrogenating step as a reaction diluent, but its use is not mandatory.
According to conventional polymerization methods, the crude vinylphenol is subjected to a purification step to separate purified p-vinylphenol.
P-Vinylphenol is a very unstable monomer, and it is very difficult, if not impossible, to purify and separate p-vinylphenol, partly because no suitable polymerization inhibitor for p-vinylphenol has been found. Such purification and separation are also very expensive.
The purified p-vinylphenol separated is then polymerized, and the desired polymer is separated from the polymerization product and purified. In other words, according to conventional techniques of preparing polymers, the preparation of a high purity p-vinylphenol polymer requires a number of steps comprising purifying crude p-ethylphenol, dehydrogenating the purified p-ethylphenol, purifying the crude p-vinylphenol obtained from the dehydrogenating, polymerizing the purified p-vinylphenol, and separating the polymer from the polymerization and purifying it. Furthermore, since the above method includes the steps of purifying the crude p-ethylphenol and the crude p-vinylphenol, which are complicated and very difficult, it is disadvantageous from the standpoint of cost.